436 



BORING 



attached by ft chain to the three legs, and the other coupled to the top of the rods ; 

 the elasticity of the india-rubber is thus brought to play upon the motion of the rods. 

 Horizontal Boriiig by Hand. For boring in the sides of mountains, quarries, or 

 other places whore long horizontal holes are required, the machine illustrated by 

 fig. 176, is sometimes used. The rods, chisels, pumps, &c., are all of the same de- 

 scription as those used for vertical boring, except that they are of somewhat lighter 



177 



make. The rods are drawn out of the hole by means of the rope A, the weight c, 



which hangs in a small pit suspended by the rope B, being raised at the same time. 



The rope A is then slipped, and the falling weight c drives the rods into the hole again. 



The rods are kept steady and horizontal by being caused to run over a small roller 



fixed on the frame, and also by moving in a slide block, adjusted by a screw and nut. 

 After using the chisel for a short time, the rods are withdrawn, and the pump or 



scourer introduced to clear away the debris, the other work being carried on as with 



ordinary vertical hand-boring. 



Boring by Steam Power. Where boreholes are required of any considerable depth, 



and where speed is of importance, hand-labour has been superseded in recent years 



in a variety of modes ; the best of 

 which is probably the system largely 

 adopted in America in searching for 

 petroleum. This machine, which is 

 shown by fig. 177, is driven by a small 

 engine, and consists of a lover or 

 wooden beam, connected at one end to 

 a small crank with a reducing slide, by 

 means of which the stroke can be made 

 either short or long. 



The chisels used are screwed into 

 a connecting piece, which is attached 

 to an iron-wire rope, and which is 

 constructed with a slide (see fig. 34, 

 p. 439), so that after the chisel strikes 

 the bottom of the hole, the top part of 

 the connecting rod slides down, keeping 

 the rope taut in the hole ; when again 



lifted up, it rises until it catches the part to which the chisel is connected. This 

 apparatus prevents the rope from becoming slack in the hole when the tool falls. 



